The important thing in all of this is that you understand all the commands you're running, and the reasoning behind them, so you end up with something secure that meets your requirements. Then, you need to stay on top of patches - it's not enough to simply go "that's secured now", dust off your hands, and move on. Your server will get hacked.

One other thing: A lot of guides suggest installing from source. I'd suggest you ignore them to start with. Install using yum, then subscribe to CentOS announce list (google "centos announce") to hear about security upgrades you need to apply. You don't want to have to track all the Apache/PHP/MyWql mailing lists and recompile from scratch every time there's a patch that needs applying - that's what package managers are for.

Of course, if the server you're installing onto isn't actually internet facing, you can ignore everything past the point where you get the working LAMP stack =)